This invention relates to setting mechanisms for liner hangers and more particularly to a setting mechanism which provides for full bore fluid flow prior to and after the liner hanger has been set to engage casing in the wellbore and suspend the liner therefrom.
In the construction of oil and gas wells, a wellbore is drilled into one or more subterranean formations or zones containing oil and/or gas to be produced. In most instances, after the wellbore is drilled, the drill string is removed and a casing string is run into the wellbore. During casing running operations, the casing must be kept filled with fluid to prevent excessive fluid pressure differentials across the casing string and to prevent blowouts. One manner of adding fluid to a casing string is by providing well casing fill apparatus which can be utilized at or near the bottom end of the casing string to allow well fluid in the wellbore to enter the interior of the casing while it is being run. One particularly useful casing fill apparatus is disclosed in U.S. Pat. No. 5,641,021 to Murray et al., issued Jun. 24, 1997, assigned to the assignee of the present invention, the details of which are incorporated herein by reference.
A liner, which simply refers to casing having a smaller outer diameter than the inner diameter of a casing that has already been cemented into a portion of the wellbore, is used for a number of reasons, and typically extends from the bottom end of the existing casing downward into the uncased portion of the wellbore. The liner will typically include float equipment such as float shoes and float collars at or near the lower end thereof. The liner is lowered on a work string having a smaller diameter than the liner. The work string may have holes or ports defined therethrough so that fluid entering the liner through casing fill apparatus like that set forth above can pass therethrough. Such an arrangement alleviates surge pressure that may occur when the liner is lowered into the wellbore and prevents, or at least reduces the possibility of damage to a formation from pressure caused by lowering the liner into the wellbore. Such an arrangement is shown in U.S. patent application Ser. No. 09/106,484, filed Jun. 29, 1998, which is assigned to the assignee of the present application, and the details of which are incorporated herein by reference.
The liner assembly may also include pump down wiper plugs which separate, or serve as the interface between, the wet cement from the fluid it is displacing, or the fluid which is being used to pump the wet cement to the desired level. A wiper plug also wipes off the inner surface of the pipe string as it passes, and prevents back flow while the cement is setting up. Although oftentimes only one wiper plug is used, it is preferred to use a bottom and a top wiper plug. Such an arrangement is shown in U.S. Pat. No. 5,413,172, issued May 9, 1995, to Laurel, the details of which are incorporated herein by reference.
The work string includes a running tool, which is known in the art, that attaches to the liner and is utilized to lower the liner into the wellbore. A liner hanger is connected to and disposed about the running tool and work string. There are a number of types of liner hangers, including liner hangers that are hydraulically set or actuated. Hydraulically set liner hangers typically include slips that expand outwardly to engage casing and suspend a liner in a wellbore. Such hydraulically set, or hydraulically actuated liner hangers are well known in the art.
Hydraulic set liners are actuated by increasing the pressure inside the work string to a desired setting pressure which causes slips or other anchoring mechanism to expand into and engage the casing. One prior art setting mechanism simply comprises a setting sleeve with a ball seat positioned in the liner above the float equipment and below the pump down wiper plugs. In order to set the liner hanger, a ball is simply displaced downward through the work string and the liner until it engages the ball seat. Pressure is increased to the setting pressure at which time the liner hanger is actuated to engage the casing and suspend the liner from the casing. The pressure can then be increased which will cause the ball, and sometimes the setting sleeve, to be displaced downward through the float equipment at the bottom of the liner. Although such an arrangement works well to set the liner, there are disadvantages. Float equipment is limited to flapper-type valves which historically are subject to failure by erosion of the valve during circulation and cement placement. Further, the minimum inner diameter through which the liner and work string must fill while running in the hole is the small inner diameter of the setting sleeve. Such a restriction can create high hydraulic forces on open formations which may exceed their fracture gradient, cause potential lost circulation problems, have blowout potential, and may damage productive formations. The restriction also causes the liner to be run more slowly than is desired, especially in circumstances involving close clearance between the liner/liner hanger and the parent casing in which the hanger is to be set. Most liner cementing plug systems which utilize such a setting sleeve are limited to a top plug only for hydraulic set systems. Enhanced fill mechanisms like that described in U.S. Pat. No. 5,641,021 issued Jun. 24, 1997 to Sullaway et al., the details of which are incorporated herein by reference cannot be used because of incompatibilities between the enhanced fill mechanism and the setting sleeve. Finally, such a setting mechanism must be activated prior to conducting cementing operations.
Another manner of setting hydraulically actuated liner is to provide a seat in the work string below the liner hanger and above any pump down wiper plugs. A solid plug or ball may be dropped into the seat and pressure increased to the setting pressure. One difficulty with such an arrangement, however, is that the liner hanger can be set only after cementing operations have been performed, since once the plug is dropped into the work string there is no flow passage through which cement can be displaced to set the liner in the wellbore.
Thus, there is a need for a setting mechanism which can be utilized to set a hydraulically set liner either before or after cementing operations have been conducted. Furthermore, there is a need for a setting mechanism which can be utilized to set such a liner and which will allow the use of enhanced casing fill-up apparatus and that will allow the use of two plug cementing plug sets. There is also a need for a setting mechanism which will allow for high circulation rates through the liner without damaging the formation.